Living organisms have been shown to exhibit circadian rhythms that provide for built in natural biological processes and behaviors. The circadian rhythm of a living organism can be influenced by many variables, including exposure to light (e.g., sunlight), such as a day/night cycle. For instance, exposure to light during the course of a 24 hour day to night period can entrain an asynchronous circadian rhythm of a living organism to the 24 hour period. Disruptions in exposure to typical light patterns during a day/night cycle can lead to disruption in the circadian rhythm. Exposure to light from artificial light sources throughout the day may have an effect on the circadian rhythm of any living organism. For instance, providing daily patterns of varying degrees in illumination throughout the day (e.g., varying intensity and/or color temperature) can be shown to positively support a more natural circadian cycle, and to provide a degree of “normality” and a physiological basis of time to an otherwise abnormal illuminated environment.
Different light sources may exhibit different spectral power distributions in illumination of light and as such may provide varying degrees of circadian entrainment. The spectral power distribution of a light source can demonstrate the radiant power emitted by the light source at each wavelength (e.g., color) over the visible electromagnetic radiation spectrum. The spectral power distribution of incandescent light sources, fluorescent light sources, metal halide light sources, etc. is mostly static and can provide limited flexibility in spectral power distribution. These sources can vary greatly from natural light found in the natural world under normal circumstances.
Light emitting diode (LED) lighting systems can include one or more LED devices that become illuminated as a result of the movement of electrons through a semiconductor material. LED devices are becoming increasingly used in many lighting applications and have been integrated into a variety of products, such as light fixtures, flashlights, and other illumination products. LED lighting systems can provide increased efficiency, life and durability, can produce less heat, and can provide other advantages relative to traditional incandescent and fluorescent lighting systems. Moreover, the efficiency of LED lighting systems has increased such that the same or similar light output can be provided at lower operational cost to the consumer in comparison to legacy light sources.
LED devices can provide greater flexibility in providing illumination with a desired spectral power distribution relative to other light sources, such as incandescent, fluorescent, and other legacy light sources. More particularly, LED devices can be provided in a range of different monochromatic colors and/or color temperatures. The color temperature of an LED device refers to the absolute temperature of a black body radiator having a chromaticity equal to that of the LED device. LED devices associated with higher color temperatures can provide a more bluish color while LED devices associated with lower color temperatures can provide a more yellowish color.